The goals of this proposal are to examine the integration and regenerative capacity of adult-born telencephalic neurons using zebrafish models of conditional gene expression and brain injury. Neural stem/progenitor cells (NPCs) and neurogenesis persist throughout life in the adult vertebrate subventricular zone (SVZ)-olfactory bulb pathway, but the regulation and biological function of adult-born neurons are poorly understood. This neurogenic pathway in mammals is stimulated by stroke and other brain injuries. SVZ neuroblasts are diverted from their normal olfactory bulb target to the injured striatum and differentiate into neurons with an apparent striatal phenotype. NPCs in the adult therefore appear to contribute to a regenerative response that, if augmented, may improve recovery from forebrain injuries. The consequences of injury-induced SVZ neurogenesis remain obscure, however, as little progress has been made in establishing the long-term survival and functional integration of adult-born neurons after brain insults. Zebrafish is an attractive, albeit underutilized, model system for the study of adult neurogenesis in the intact or injured forebrain. The central nervous system (CNS) regenerative response of adult teleost fish, including zebrafish, is much more robust than in mammals. Understanding how regeneration is achieved after brain injury in the zebrafish is likely to provide insight into why mammalian CNS regeneration is limited, and how this limitation might be reversed to achieve restorative NPC therapies. These and other advantages of the zebrafish system have led our group and others to begin characterizing SVZ-olfactory bulb neurogenesis in adult zebrafish. Our data suggest that adult-born neurons integrate in the bulb and that SVZ neurogenesis is stimulated by excitotoxin-induced telencephalic injury. We also have begun developing inducible transgenic zebrafish lines for fate mapping to examine the long-term integration of adult-born telencephalic neurons. Using these lines and the excitotoxic forebrain injury model, we propose to test the following hypotheses: 1) Adult-born SVZ neuroblasts migrate to the olfactory bulb and generate olfactory neurons that integrate into preexisting networks;and 2) Excitotoxic telencephalic injury stimulates adult SVZ neurogenesis to replace damaged neurons. Two specific aims are proposed to test these hypotheses. In Aim 1, transgenic zebrafish lines with inducible Cre recombinase under the control of NPC-specific promoters will be crossed with a reporter line to conditionally label adult-born neurons in the telencephalic SVZ and examine their structural and functional integration. In Aim 2, fish will undergo excitotoxic telencephalic lesioning to determine whether injury stimulates the proliferation, migration, and long-term integration of adult-born neurons identified by mitotic labeling or transgenic approaches. These studies will shed light on the long-term fate and regenerative potential of adult-born forebrain NPCs and will provide valuable tools to study adult neurogenesis in the intact and injured vertebrate forebrain. PUBLIC HEALTH RELEVANCE: Neural stem cells and the birth of new nerve cells persist in the adult brain. These cells have therapeutic potential and may be stimulated to repair the brain after injury. The reasons why repair is often incomplete after acute brain insults are unknown, but zebrafish have a greater nervous system regenerative capacity than mammals and may shed light on the factors that limit repair. Because the same pathways of nerve cell birth are present in the forebrains of zebrafish and mammals, progress in understanding neural stem cell behavior in the intact or injured fish brain may lead to therapies for neural repair after stroke or other brain insults.